P-Doped NiCo₂S₄/CoZn-LDH Layered Heterostructures: Synergistically Improved Conductivity and Enhanced OH^- Adsorption for High-Performance Asymmetric Supercapacitors

Doping induces lattice distortion and modifies the electronic structure of materials, thereby enhancing their electrical conductivity and chemical stability. The built-in electric field at heterojunction interfaces further promotes charge carrier migration and improves surface reaction kinetics. To leverage these synergistic effects, this study employs a combined approach involving sulfidation, phosphidation, and electrodeposition to achieve P-doping and construct a heterojunction layered structure. Specifically, P-doping is implemented through a phosphorization treatment of NiCo₂S₄ grown on nickel foam, followed by the electrodeposition of CoZn-layered double hydroxide (LDH) onto the honeycomb-like NiCo₂S₄ substrate. Density Functional Theory calculations demonstrate that this unique structural design markedly enhances the composite's electrical conductivity and optimizes the adsorption energy of OH^- ions, leading to significantly improved ion/electron reaction kinetics. The resulting P-NiCo₂S₄@CoZn-LDH electrode exhibits a high areal capacitance of 15.00 F cm^-2 at a current density of 5 mA cm^-2. When assembled into an asymmetric supercapacitor (P-NiCo₂S₄@CoZn-LDH//activated carbon (AC)), the device achieves an energy density of 53.75 Wh kg^-1 at a power density of 205.76 W kg^-1, while maintaining 77.36% capacitance retention after 10 000 cycles. These findings highlight the synergistic benefits of doping and heterojunction engineering in enhancing charge transport and ion adsorption capabilities, offering a promising strategy for developing high-performance supercapacitors.